Mobile phones usually have antennas that are required to cover many frequency bands. For example, the GSM antenna may have to cover four bands, namely the two European bands called GSM 900 (880-960 MHz) and GSM 1800 (1710-1880 MHz), and two US bands called GSM 850 (824-894 MHz) and GSM 1900 (1850-1990 MHz). It is advantageous and desirable to provide an antenna which can be tuned between two states, wherein the European state covers GSM 900 and GSM 1800 and the US state covers GSM 850 and GSM 1900, for example.
Furthermore, it is advantageous to provide an antenna which can be tuned to optimize the antenna performance in different use situations. For example, the impedance of a mobile phone antenna may be detuned when the mobile phone is put next to the head of the user or covered by the user's hand. Also, the antenna operation may change when the phone is put on a table or inside a bag, or when the phone has moving parts with the parts located differently relative to each other. In many of these situations, the antenna may be required tuning in order to improve the antenna performance.
Similar applications of tunable antennas exist for base station antennas, access points and other wireless communication devices.